Polythiophenes and devices thereof

ABSTRACT

A polythiophene wherein the monomer segments thereof contain 
                         
wherein A is a side chain; B is hydrogen or a side chain; and D is a divalent segment, and wherein the number of A-substituted thienylene units (I) in the monomer segments is from about 1 to about 10, the number of B-substituted thienylene units (II) is from 0 to about 5, and the number of divalent segments D is 0 or 1.

This is a continuation of U.S. patent application Ser. No. 10/042,360,filed Jan. 11, 2002, now U.S. Pat. No. 6,872,801.

COPENDING APPLICATIONS

Illustrated in applications U.S. Ser. No. 10/042,358, now U.S. Pat. No.6,770,904, U.S. Ser. No. 10/042,342, filed Jan. 11, 2002, U.S. Ser. No.10/042,356, now U.S. Pat. No. 6,621,099, U.S. Ser. No. 10/042,357, filedJan. 11, 2002, and U.S. Ser. No. 10/042,360, now U.S. Pat. No.6,872,801, the disclosures of which are totally incorporated herein byreference, and filed concurrently herewith, are polythiophenes anddevices thereof. The appropriate components, processes thereof and usesthereof illustrated in these copending applications may be selected forthe present invention in embodiments thereof.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of NIST ContractNo. 70NANBOH3033.

BACKGROUND

The present invention is generally directed to polythiophenes and usesthereof. More specifically, the present invention in embodiments isdirected to a class of polythiophenes comprised of monomer segmentscontaining at least two different types of 2,5-thienylene units and anoptional divalent moiety, and which polythiophenes are capable ofmolecular self-organization, providing ordered microstructures in thinfilms that can be ideal for microelectronic device applications. Anexample of such polythiophenes include certain thienylene moieties withlong side chains, which are arranged in a regioregular manner on thepolymer chain, and which can assist to induce and to facilitatemolecular organization of the polythiophenes.

Semiconductive polymers like certain polythiophenes, which are useful asactive semiconductor materials in thin film transistors (TFTs), havebeen reported. A number of these polymers have some solubility inorganic solvents and are thus able to be fabricated as semiconductorchannel layers in TFTs by solution processes, such as spin coating,solution casting, dip coating, screen printing, stamp printing, jetprinting and the like. Their ability to be fabricated via commonsolution processes would render their manufacturing simpler and costeffective as compared to the costly conventional photolithographicprocesses typical of silicon-based devices such as hydrogenatedamorphous silicon TFTs. Moreover, desired are transistors fabricatedwith polymer materials, such as polythiophenes, referred to as polymerTFTs, with excellent mechanical durability and structural flexibility,which may be highly desirable for fabricating flexible TFTs on plasticsubstrates. Flexible TFTs would enable the design of electronic deviceswhich usually require structural flexibility and mechanical durabilitycharacteristics. The use of plastic substrates together with organic orpolymer transistor components can transform the traditionally rigidsilicon TFT into a mechanically more durable and structurally flexiblepolymer TFT design. The latter is of particular value to large areadevices such as large area image sensors, electronic paper and otherdisplay media. Also, the selection of polymer TFTs for integratedcircuit logic elements for low end microelectronics, such as smartcards, radio frequency identification (RFID) tags, and memory/storagedevices, may also greatly enhance their mechanical durability, and thustheir useful life span. Nonetheless, many of the semiconductorpolythiophenes are not, it is believed, stable when exposed to air asthey become oxidatively doped by ambient oxygen, resulting in increasedconductivity. The result is larger off-current and thus lower currenton/off ratio for the devices fabricated from these materials.Accordingly, with many of these materials, rigorous precautions have tobe undertaken during materials processing and device fabrication toexclude environmental oxygen to avoid or minimize oxidative doping.These precautionary measures add to the cost of manufacturing thereforeoffsetting the appeal of certain polymer TFTs as an economicalalternative to amorphous silicon technology, particularly for large areadevices. These and other disadvantages are avoided or minimized inembodiments of the present invention.

REFERENCES

A number of organic semiconductor materials has been described for usein field-effect TFTs, which materials include organic small moleculessuch as pentacene, see for example D. J. Gundlach et al., “Pentaceneorganic thin film transistors—molecular ordering and mobility”, IEEEElectron Device Lett., Vol. 18, p. 87 (1997), to oligomers such assexithiophenes or their variants, see for example reference F. Garnieret al., “Molecular engineering of organic semiconductors: Design ofself-assembly properties in conjugated thiophene oligomers”, Amer. Chem.Soc., Vol. 115, p. 8716 (1993), and certain polythiophenes, such aspoly(3-alkylthiophene), see for example reference Z. Bao et al.,“Soluble and processable regioregular poly(3-hexylthiophene) forfield-effect thin film transistor application with high mobility”, Appl.Phys. Lett. Vol. 69, p 4108 (1996). Although organic material based TFTsgenerally provide lower performance characteristics than theirconventional silicon counterparts, such as silicon crystal orpolysilicon TFTs, they are nonetheless sufficiently useful forapplications in areas where high mobility is not required. These includelarge area devices, such as image sensors, active matrix liquid crystaldisplays and low end microelectronics such as smart cards and RFID tags.TFTs fabricated from organic or polymer materials may be functionallyand structurally more desirable than conventional silicon technology inthe aforementioned areas in that they may offer mechanical durability,structural flexibility, and the potential of being able to beincorporated directly onto the active media of the devices, thusenhancing device compactness, for transportability. However, most smallmolecule or oligomer-based devices rely on difficult vacuum depositiontechniques for fabrication. Vacuum deposition is selected primarilybecause the small molecular materials are either insoluble or theirsolution processing by spin coating, solution casting, or stamp printingdo not generally provide uniform thin films. In addition, vacuumdeposition may also involve the difficulty of achieving consistent thinfilm quality for large area format. Polymer TFTs, such as thosefabricated from regioregular polythiophenes of, for example,regioregular poly(3-alkylthiophene-2,5-diyl) by solution processes,while offering reasonably good mobility, suffer from their propensitytowards oxidative doping in air. For practical low cost TFT design, itis therefore of value to have a semiconductor material that is bothstable and solution processable, and where its performance is notadversely affected by ambient oxygen, for example, regioregularpolythiophenes such as poly(3-alkylthiophene-2,5-diyl) are verysensitive to air. The TFTs fabricated from these materials in ambientconditions generally exhibit very large off-current, very low currenton/off ratios, and their performance characteristics degrade rapidly.

References that may be of interest include U.S. Pat. Nos. 6,150,191;6,107,117; 5,969,376; 5,619,357, and 5,777,070.

SUMMARY

It is a feature of the present invention to provide semiconductorpolymers, such as polythiophenes, which are useful for microelectronicdevice applications, such as thin film transistor devices.

It is another feature of the present invention to provide polythiopheneswhich are soluble in common organic coating solvents such as, forexample, methylene chloride, tetrahydrofuran, toluene, xylene,mesitylene, chlorobenzene, and the like, and thus can be fabricated bysolution processes such as spin coating, screen printing, stampprinting, dip coating, solution casting, jet printing and the like.

Another feature of the present invention resides in providing electronicdevices, such as TFTs with a polythiophene channel layer, and whichlayer has a conductivity of from 10⁻⁶ to about 10⁻⁹ S/cm(Siemens/centimeter).

A further feature of the present invention is to provide polythiopheneswhich are accessible synthetically, and which polythiophenes possessenhanced resistance to oxidative doping by ambient oxygen.

Also, in yet another feature of the present invention there are providedpolythiophenes and devices thereof, and which devices exhibit enhancedresistance to the adverse effects of oxygen, that is, these devicesexhibit relatively high current on/off ratios, and their performancedoes not usually degrade as rapidly as those fabricated fromregioregular polythiophenes such as regioregularpoly(3-alkylthiophene-3,5-diyl).

Additionally, in a further feature of the present invention there isprovided a class of polythiophenes with unique structural features whichare conducive to molecular self-alignment under appropriate processingconditions and which structural features also enhance the stability ofdevice performance. Proper molecular alignment can result in highermolecular structural order in thin films, which can be important toefficient charge carrier transport, and thus higher electricalperformance.

Aspects of the present invention relate to a polythiophene

wherein A is a side chain; B is hydrogen or a side chain; D is adivalent linkage; a and c represent the number of A-substitutedthienylenes; b is the number of B-substituted thienylenes; d is 0 or 1;and n represents the degree of polymerization or the number of themonomer segments; a polythiophene wherein A contains from 5 to about 25carbon atoms in length; B is hydrogen or short side chain containing,for example, from 1 to about 4 carbon atoms; D is optionally comprisedof a saturated moiety of alkylene, —O—R—O—, —S—R—S—, —NH—R—NH—, whereinR is alkylene or arylene, or an unsaturated moiety of arylene orheteroaromatics; a is from about 1 to about 8 and c is from 0 to about8, and b is from zero to about 6; a polythiophene represented by

and wherein n represents the number of segments; a polythiophene whereinthe polythiophene is represented by the following formulas

a polythiophene wherein A is alkyl, and B is alkyl; a polythiophenewherein A is alkyl containing from about 1 to about 25 carbon atoms, andB is hydrogen or a short alkyl containing from 1 to about 4 carbonatoms; a polythiophene wherein A contains from about 5 to about 25carbon atoms, and B contains from about 1 to about 4 carbon atoms; apolythiophene wherein a is from about 1 to about 7; a polythiophenewherein b is from about 1 to about 7; a polythiophene wherein d is zero;a polythiophene wherein d is 1; a polythiophene wherein n is from about5 to about 5,000; a polythiophene wherein n is from about 5 to about3,000; a polythiophene wherein n is from about 2,000 to about 4,000; apolythiophene wherein A is alkyl containing from about 6 to about 25carbon atoms; B is hydrogen or alkyl containing from 1 to about 3 carbonatoms; D is arylene or dioxyarene, each containing from about 6 to about40 carbon atoms, or alkylene or dioxyalkane, each containing from about1 to about 20 carbon atoms; a polythiophene wherein A is alkylcontaining from about 6 to about 12 carbon atoms, and B is a hydrogenatom; a polythiophene wherein A is alkyl containing from 5 to about 15carbon atoms; B is a hydrogen atom; D is arylene; a, b, c, and m areindependently selected from the numbers 1, 2, and 3; and d=1; apolythiophene wherein A is alkyl containing from about 6 to about 12carbon atoms; B is a hydrogen atom; D is arylene; a=c=m=1; b=2; and d=1;a polythiophene wherein n is from about 5 to about 5,000; apolythiophene wherein the number average molecular weight (M_(n)) of(III) is from about 10,000 to about 30,000, and the weight averagemolecular weight (M_(w)) is from about 15,000 to about 100,000; apolythiophene wherein the number average molecular weight (M_(n)) of(III) is from about 2,000 to about 100,000, and wherein the weightaverage molecular weight (M_(w)) is from about 4,000 to about 500,000,each as measured by gel permeation chromatography using polystyrenestandards; a polythiophene wherein A is hexyl heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, or pentyldecyl; apolythiophene wherein D is an arylene selected from the group consistingof phenylene, tolylene, xylylene, biphenylene, substituted biphenylene,fluorenylene, phenanthrenylene, dihydrophenanthrenylene,dibenzofuranediyl, dibenzothiophenediyl, and carbazole-diyl; apolythiophene wherein D is saturated linkage selected from the groupconsisting of alkylene, dioxyalkane, dioxyarene, and oligoethyleneoxide; a polythiophene wherein the polythiophene is represented by orencompassed by the following formulas, and wherein n represents thenumber of repeating segments, and is a number of from about 5 to about4,000

a polythiophene wherein the polythiophene is

a polythiophene wherein the monomer segments thereof contain

wherein A is a side chain; B is hydrogen or a side chain; and D is adivalent linkage, and wherein the number of A-substituted thienyleneunits (I) in the monomer segment is from about 1 to about 10, the numberof B-substituted thienylene units (II) is from 0 to about 5, and thenumber of divalent linkage D is 0 or 1; and polythiophenes generatedfrom a monomer segment containing two types of 2,5-thienylene units, (I)and (II) and a divalent linkage D in suitable proportions

wherein A is a long side chain containing, for example, about 5 to about25 atoms in length; B is hydrogen atom or a short side chain containing,for example, less than or about 4 carbon atoms in length, and morespecifically, from about 1 to about 3 carbon atoms in length; and D is adivalent unit such as a saturated moiety of, for example, methylene,ethylene, propylene, butylene, pentylene and the like, or an unsaturatedmoiety of, for example, aryl, such as arylene biarylene, fluorenylene,and the like. The number of A-substituted thienylene units (I) in themonomer segments can, for example, be from about 1 to about 10, thenumber of B-substituted thienylene units (II) can be from 0 to about 5;and the number of divalent segment D can be, for example, 0 or 1.

The polythiophenes of the present invention in embodiments can beillustrated by Formula (III)

wherein A is a long side chain containing, for example, 5 to 25 atoms inlength; B is hydrogen atom or a short side chain containing, for example4 or less than about 4 carbon atoms in length; D is a divalent segment,such as saturated moiety, such as an alkylene like methylene, ethylene,propylene, and the like, or an unsaturated moiety like arylene,biarylene, fluorenylene, and the like; a and c are the number ofA-substituted thienylenes with a being, for example, from about 1 toabout 8 and c being, for example, from 0 to about 8; b is the number ofB-substituted thienylene units and can be, for example, from 0 to about5; d is, for example, 0 or 1; and n is the degree of polymerization orthe number of the monomer segments in the polythiophene (III), and canbe, for example, from about 5 to over 5,000, and more specifically, fromabout 10 to about 1,000. The number average molecular weight (M_(n)) ofthe polythiophenes of the present invention can be, for example, fromabout 2,000 to about 100,000, and more specifically, from about 4,000 toabout 50,000, and their weight average molecular weight (M_(w)) can befrom about 4,000 to about 500,000, and more specifically, from about5,000 to about 100,000 both as measured by gel permeation chromatographyusing polystyrene standards.

Examples of A include alkyl containing, for example, from about 5 toabout 30 carbon atoms, such as pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentyldecyl, and thelike, alkoxyalkyl, such as for example methoxybutyl, methoxyhexyl,methoxyhexyl, methoxyheptyl, and the like, a polyether chain, such aspolyethylene oxide, perhaloalkyl, such as perfluoroalkyl, a polysiloxychain, such as a trialkylsiloxyalkyl derivative, and the like; examplesof B include hydrogen, halogen or halide, such as chloro, fluoro, orbromo atoms, alkyl like methyl, ethyl, propyl, alkoxy, such as methoxy,ethoxy, propoxy, butoxy and the like. Examples of the divalent linkage Dare alkylene, such as methylene, ethylene, dialkylmethylene, propylene,and the like; arylene such as phenylene, biphenylene, phenanthrenylene,dihydrophenanthrenylene, fluorenylene, oligoarylene, and the like; anddioxyalkylene, dioxyarylene, oligoethylene oxide, and the like.

Specific illustrative polythiophenes include the following, and whereinn represents the number of segments

The polythiophenes of the present invention in embodiments are solublein common organic coating solvents, for example they possess asolubility of at least about 0.1 percent by weight, and morespecifically, from about 0.5 percent to about 5 percent by weight insuch solvents as methylene chloride, 1,2-dichloroethane,tetrahydrofuran, toluene, xylene, mesitylene, chlorobenzene, and thelike. Moreover, the polythiophenes of the present invention inembodiments when fabricated as semiconductor channel layers in thin filmtransistor devices provide a stable conductivity of, for example, fromabout 10⁻⁹ S/cm to about 10⁻⁶ S/cm, and more specifically, from about10⁻⁸ S/cm to about 10⁻⁷ S/cm as determined by conventional four-probeconductivity measurements.

A number of synthetic procedures are suitable for the preparation of thepolythiophenes of the present invention, each depending primarily on thespecific polythiophenes desired. For example, polythiophene (V), amember of the polythiophene class represented by general Formula (III)with a=c=d=m=1, B═H, and D=Ar (arylene), can be prepared from the Suzukicoupling reaction of a properly constructed oligothiophene monomer (IVb)with an appropriate arylenediboronate. Specifically, (IVb) can beobtained from bromination of (IVa), which in turn is obtained from thereaction of 2-bromo-3-alkylthiophene and oligothiophenedibromide,reference Scheme 1. The Suzuki coupling polymerization is generallyaccomplished by heating with stirring a mixture of equal molarequivalents of (IVb) and arylene-diboronate in a suitable solvent, suchas toluene, in the presence of about 2 to about 6 molar percent oftetrakis(triphenylphosphine)-palladum, about 2 to about 4 molarequivalent of an inorganic base, such as sodium carbonate, in the formof a 1M to 2M aqueous solution, and about 1 to 5 mole percent of a phasetransfer catalyst, such as tetrabutylamomonium chloride ortricaprylylmethylammonium chloride at a temperature of, for example,from about 80° C. to about at about 100° C. under an inert atmosphere.After the polymerization, the polythiophene product, such as (V), isisolated by precipitation from methonol, optionally followed by soxhletextraction with appropriate solvents such as methanol, toluene, andchlorobenzene.

In embodiments and with further reference to the present invention, thesubstrate layer may generally be a silicon material inclusive of variousappropriate forms of silicon, a glass plate, a plastic film or a sheet,and the like depending on the intended applications. For structurallyflexible devices, a plastic substrate, such as for example polyester,polycarbonate, polyimide sheets, and the like, may be selected. Thethickness of the substrate may be, for example, from about 10micrometers to over 10 millimeters with a specific thickness being fromabout 50 to about 100 micrometers, especially for a flexible plasticsubstrate and from about 1 to about 10 millimeters for a rigid substratesuch as glass or silicon.

The insulating dielectric layer, which can separate the gate electrodefrom the source and drain electrodes, and in contact with thesemiconductor layer, can generally be an inorganic material film, anorganic polymer film, or an organic-inorganic composite film. Thethickness of the dielectric layer is, for example, from about 10nanometers to about 1 micrometer with a more specific thickness beingabout 100 nanometers to about 500 nanometers. Illustrative examples ofinorganic materials suitable as the dielectric layer include siliconoxide, silicon nitride, aluminum oxide, barium titanate, bariumzirconate titanate, and the like; illustrative examples of organicpolymers for the dielectric layer include polyesters, polycarbonates,poly(vinyl phenol), polyimides, polystyrene, poly(methacrylate)s,poly(acrylate)s, epoxy resin, and the like; and illustrative examples ofinorganic-organic composite materials include nanosized metal oxideparticles dispersed in polymers such as polyester, polyimide, epoxyresin and the like. The insulating dielectric layer is generally of athickness of from about 50 nanometers to about 500 nanometers dependingon the dielectric constant of the dielectric material used. Morespecifically, the dielectric material has a dielectric constant of, forexample, at least about 3, thus a suitable dielectric thickness of about300 nanometers can provide a desirable capacitance, for example, ofabout 10⁻⁹ to about 10⁻⁷ F/cm².

Situated, for example, between and in contact with the dielectric layerand the source/drain electrodes is the active semiconductor layercomprised of the polythiophenes illustrated herein, and wherein thethickness of this layer is generally, for example, about 10 nanometersto about 1 micrometer, or about 40 to about 100 nanometers. This layercan generally be fabricated by solution processes, such as spin coating,casting, screen, stamp, or jet printing of a solution of thepolythiophenes of the present invention.

The gate electrode can be a thin metal film, a conducting polymer film,a conducting film generated from a conducting ink or paste, or thesubstrate itself (for example heavily doped silicon). Examples of gateelectrode materials include but are not limited to aluminum, gold,chromium, indium tin oxide, conducting polymers, such as polystyrenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PSS/PEDOT), aconducting ink/paste comprised of carbon black/graphite or colloidalsilver dispersion contained in a polymer binder, such as ELECTRODAGavailable from Acheson Colloids Company and silver filled electricallyconductive thermoplastic ink available from Noelle Industries, or thelike. The gate layer can be prepared by vacuum evaporation, sputteringof metals or conductive metal oxides, coating from conducting polymersolutions or conducting inks or dispersions by spin coating, casting orprinting. The thickness of the gate electrode layer is, for example,from about 10 nanometers to about 10 micrometers, and a specificthickness is, for example, from about 10 to about 200 nanometers formetal films and about 1 to about 10 micrometers for polymer conductors.

The source and drain electrode layer can be fabricated from materialswhich provide a low resistance ohmic contact to the semiconductor layer.Typical materials suitable for use as source and drain electrodesinclude those of the gate electrode materials such as gold, nickel,aluminum, platinum, conducting polymers, and conducting inks. Typicalthickness of this layer is about, for example, from about 40 nanometersto about 1 micrometer with the more specific thickness being about 100to about 400 nanometers. The TFT devices contain a semiconductor channelwith a width W and length L. The semiconductor channel width may be, forexample, from about 10 micrometers to about 5 millimeters with aspecific channel width being about 100 micrometers to about 1millimeter. The semiconductor channel length may be, for example, fromabout 1 micrometer to about 1 millimeter with a more specific channellength being from about 5 micrometers to about 100 micrometers.

The source electrode is grounded and a bias voltage of generally about 0volt to about 80 volts is applied to the drain electrode to collect thecharge carriers transported across the semiconductor channel when avoltage of generally about +10 volts to about −80 volts is applied tothe gate electrode.

The following Examples are provided.

GENERAL PROCEDURE

a) Device Fabrication:

There was selected a top-contact thin film transistor configuration asthe primary test device structure.

The test device was comprised of an n-doped silicon wafer with athermally grown silicon oxide layer of a thickness of about 110nanometers thereon. The wafer functioned as the gate electrode while thesilicon oxide layer acted as the gate dielectric and had a capacitanceof about 32 nF/cm² (nanofarads/square centimeter). The fabrication ofthe device was accomplished in ambient conditions without taking anyprecautions to exclude the materials and device from exposure to ambientoxygen, moisture, or light. The silicon wafer was first cleaned withmethanol, air dried, and then immersed in a 0.01 M solution of1,1,1,3,3,3-hexamethyldisilazane in dichloromethane for 30 minutes atroom temperature. Subsequently, the wafer was washed withdichloromethane and dried. The test semiconductor polythiophene layer ofabout 30 nanometers to about 100 nanometers in thickness was thendeposited on top of the silicon oxide dielectric layer by spin coatingat a speed of 1,000 rpm for about 35 seconds, and dried in vacuo at 80°C. for 20 hours. The solution used in fabricating the semiconductorlayer was comprised of 1 percent by weight of the polythiophene in anappropriate solvent, and was filtered through a 0.45 μm filter beforeuse. Thereafter, the gold source and drain electrodes were deposited ontop of the semiconductor polythiophene layer by vacuum depositionthrough a shadow mask with various channel lengths and widths, thusproviding a series of transistors of various dimensions. Forconsistency, the devices after fabrication were kept in a dry atmosphereof about 30 percent relative humidity in the dark before and afterevaluation.

b) TFT Device Characterization:

The evaluation of field-effect transistor performance was accomplishedin a black box at ambient conditions using a Keithley 4200 SCSsemiconductor characterization system. The carrier mobility, μ, wascalculated from the data in the saturated regime (gate voltage,V_(G)<source-drain voltage, V_(SD)) accordingly to equation (1)I _(SD) =C _(i)μ(W/2L)(V _(G) −V _(T))  (1)where I_(SD) is the drain current at the saturated regime, W and L are,respectively, the semiconductor channel width and length, Ci is thecapacitance per unit area of the gate dielectric layer, and V_(G) andV_(T) are, respectively, the gate voltage and threshold voltage. V_(T)of the device was determined from the relationship between the squareroot of I_(SD) at the saturated regime and V_(G) of the device byextrapolating the measured data to I_(SD)=0.

Another property of a field-effect transistor is its current on/offratio. This is the ratio of the saturation source-drain current when thegate voltage V_(G) is equal to or greater than the drain voltage V_(D)to the source-drain current when the gate voltage V_(G) is zero.

COMPARATIVE EXAMPLE

A series of comparative thin film transistors were fabricated containingthe known regioregular polythiophene, poly(3-hexythiophene-2,5-diyl),which is commonly known as P3HT. This material was purchased fromAldrich Chemical and was purified by three successive precipitations ofits solution in chlorobenzene from methanol.

The devices were fabricated in ambient conditions in accordance with theprocedure as described hereinbefore. Using transistors with a dimensionof W (width)=5,000 μm and L (length)=60 μm, the following averageproperties from at least five transistors were obtained:

Mobility: 1 to 1.2×10² cm²/V.sec

Initial on-off ratio: 1.5 to 2.1×10³

On-off ratio after 5 days: 5 to 10

The observed low initial current on/off ratios are an indication of thepropensity of poly(3-hexythiophene-2,5-diyl) towards oxidative doping,that is the instability of poly(3-hexythiophene-2,5-diyl) in thepresence of ambient oxygen. The reductions in the current on/off ratiosover just a five day period further confirm the functional instabilityof poly(3-hexythiophene-2,5-diyl) in ambient conditions.

EXAMPLE

a) Preparation of Polythiophene (3):

Two monomers, 5,5′-bis(3-dodecyl-5-bromo-2-thienyl)-2,2′-dithiophene and1,4-benzenebis(pinacolboronate), selected for the preparation ofpolythiophene (3) were prepared in the following manner.

5,5′-Bis(3-dodecyl-5-bromo-2-thienyl)-2,2′-dithiophene

A solution of 2-bromo-3-dodecylthiophene (11.5 grams, 34.92 mmol) in 40milliliters of anhydrous tetrahydrofuran (THF) was added slowly over aperiod of 20 minutes to a mechanically stirred suspension of magnesiumturnings (1.26 grams, 51.83 mmol) in 10 milliliters of THF in a 100milliliter round-bottomed flask under an inert argon atmosphere. Theresultant mixture was stirred at room temperature, of about 22° C. toabout 25° C., for 2 hours and then at 50° C. for 20 minutes beforecooling down to room temperature. The resultant mixture was then addedvia a cannula to a mixture of 5,5′-dibromo-2,2′-dithiophene (4.5 grams,13.88 mmol) and [1,3-bis(diphenylphosphino)]dichloronickel (II) (0.189gram, 0.35 mmol) in 80 milliliters of anhydrous THF in a 250 milliliterround-bottomed flask under an inert atmosphere, and refluxed for 48hours. Subsequently, the reaction mixture was diluted with 200milliliters of ethyl acetate, was washed twice with water, with a 5percent aqueous hydrochloric acid (HCl) solution, and dried withanhydrous sodium sulfate. A dark brown syrup, obtained after evaporationof the solvent, was purified by column chromotography on silica gel, andfurther purified by recrystallization from a mixture of methanol andisopropanol yielding 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene in55 percent yield; m.p. 58.9° C.

The NMR spectrum of the compound was recorded at room temperature usinga Bruker DPX 300 NMR spectrometer:

¹H NMR (CDCl₃): δ 7.18 (d, J=5.4 Hz, 2H), 7.13 (d, J=3.6 Hz, 2H), 7.02(d, J=3.6 Hz, 2H), 6.94 (d, J=5.4 Hz, 2H), 2.78 (t, 4H), 1.65 (q, 1.65,4H), 1.28 (bs, 36H), 0.88 (m, 6H).

To a solution of 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene (0.61gram, 9.22×10⁴ mmol) in 35 milliliters of 3/1 dichloromethane/aceticacid in a 3-necked flask under an argon atmosphere there was added insmall portions solid N-bromosuccinimide (0.348 gram, 1.95×10⁻³ mmol)over a period of 10 to 20 minutes. After 2 hours of reaction, theprecipitated solid product was collected by filtration, andrecrystallized from a mixture of dichloromethane and methanol. The yieldwas about 79 percent, m.p., 75.6° C.

¹H NMR (CDCl₃): δ 6.9 (s, 2H), 7.10 (d, J=3.9 Hz, 2H), 6.96 (d, J=4.2Hz, 2H), 2.78 (t, 4H), 1.65 (q, 1.65, 4H), 1.28 (bs, 36H), 0.88 (m, 6H).

1,4-Benzenebis(pinacolboronate)

1.7 M of tert-butyllithium in pentane (121 milliliters, 205.7 mmol) wasadded dropwise by means of a syringe to a solution of 1,4-dibromobenzene(11.9 grams, 50.44 mmol) in 150 milliliters of anhydrous tetrahydrofuranin a 500 milliliter round-bottomed flask at about −75° C. to about −78°C. under an argon atmosphere, and allowed to react for 2 hours.2-isopropoxy-4,4′,5,5′-tetramethyl-1,3,2-dioxaborolane (65.69 grams,353.08 mmol) was then added quickly by means of a syringe, and thereaction mixture was stirred at the same temperature for an additional 2hours and then at room temperature for 12 hours. Subsequently, thereaction mixture was diluted with 150 milliliters of dichloromethane,and the solid materials were filtered off. The organic phase was washed3 times with water, dried, and evaporated to provide the above boronatecrude product which was recrystallized from hexane to provide a whitesolid in about 59 percent yield, m.p., 245.3° C.

¹H—NMR(CDCl₃): δ 7.8 (s, 4H), 1.3 (s, 24H).

Polymerization:

To a mixture of 5,5′-bis(3-dodecyl-5-bromo-2-thienyl)-2,2′-dithiophene(0.5 gram, 0.61 mmol) and 1,4-benzenebis(pinacolboronate) (0.2 gram,0.61 mmol) in 5 milliliters of toluene under an argon atmosphere wasadded a mixture of tetrakis(triphenylphosphine)-palladium (0.014 gram,0.012 mmol), ALIQUART 336 (0.2 gram) in 2 milliliters of toluene, and 2M of aqueous sodium carbonate solution (1.5 milliliters). The resultantmixture was heated at reflux with gentle stirring for 2 days.Thereafter, the reaction mixture was poured into methanol and theprecipitated polythiophene product was collected by filtration. Thepolythiophene was purified by soxhlet extration with toluene and thenprecipitated from methnol to give 0.416 gram of polythiophene (3) as adark redish solid.

b) Device Fabrication and Evaluation:

Thin film transistor devices were fabricated under ambient conditionsusing the above prepared polythiophene according to the generalprocedures illustrated herein. No precautions were taken to excludeambient oxygen or light. Using transistors of the same dimension as thatof the P3HT device (W=5,000 μm and L=60 μm), the following averageproperties from at least five transistors were obtained.

Mobility: 4.3 to 6.1×10⁻³ cm²/V.sec

Initial on-off ratio: 6.0 to 9.5×10⁵

On-off ratio after 5 days: 1.8 to 5.5×10⁵

On-off ratio after 30 days: 6.8 to 8.4×10⁴

The stability of the polythiophene semiconductor layer was demonstratedby the large initial current on/off rations and the slow reduction incurrent on/off ratio over time.

Other embodiments and modifications of the present invention may occurto those skilled in the art subsequent to a review of the informationpresented herein; these embodiments and modifications, equivalentsthereof, substantial equivalents thereof, or similar equivalents thereofare also included within the scope of this invention.

1. A polythiophene

wherein A is a side chain; B is hydrogen or a side chain; D is adivalent linkage; a and c represent the number of A-substitutedthienylenes; b is the number of B-substituted thienylene segments; d is0 or 1; and n represents the degree of polymerization or the number ofthe monomer segments.
 2. A polythiophene in accordance with claim 1wherein A contains from 5 to about 25 carbon atoms; said B side chaincontains from zero to about 4 carbon atoms; said D is optionallycomprised of a saturated moiety of alkylene, —O—R—O—, —S—R—S—,—NH—R—NH—, wherein R is alkylene or arylene, or an unsaturated moiety ofarylene or heteroaromatics; a is from about 1 to about 8 and c beingfrom 0 to about 8, and b is from zero to about
 6. 3. A polythiophene inaccordance with claim 1 wherein a is from about 1 to about
 7. 4. Apolythiophene in accordance with claim 1 wherein b is from about 1 toabout
 7. 5. A polythiophene in accordance with claim 1 wherein d iszero.
 6. A polythiophene in accordance with claim 1 wherein d is
 1. 7. Apolythiophene in accordance with claim 1 wherein n is from about 5 toabout 5,000.
 8. A polythiophene in accordance with claim 1 wherein n isfrom about 5 to about 3,000.
 9. A polythiophene in accordance with claim1 wherein n is from about 10 to about 1,000.
 10. A polythiophene inaccordance with claim 1 wherein A is alkyl containing from about 6 toabout 25 carbon atoms; B is hydrogen or alkyl containing from 1 to about3 carbon atoms; D is arylene or dioxyarene, each containing from about 6to about 40 carbon atoms, or alkylene or dioxyalkane, each containingfrom about 1 to about 20 carbon atoms.
 11. A polythiophene in accordancewith claim 1 wherein A is alkyl containing from about 8 to about 12carbon atoms, and B is a hydrogen atom.
 12. A polythiophene inaccordance with claim 1 wherein A is alkyl containing from 5 to about 15carbon atoms; B is a hydrogen atom; D is arylene; a, b, c, and m areindependently selected from the numbers 1, 2, and 3; and d=1.
 13. Apolythiophene in accordance with claim 1 wherein A is alkyl containingfrom about 8 to about 12 carbon atoms; B is a hydrogen atom; D isarylene; a=c=m=1; b=2; and d=1.
 14. A polythiophene in accordance withclaim 1 wherein the number average molecular weight (M_(n)) of (III) isfrom about 10,000 to about 30,000, and the weight average molecularweight (M_(w)) is from about 15,000 to about 100,000.
 15. Apolythiophene in accordance with claim 1 wherein the number averagemolecular weight (M_(n)) of (III) is from about 2,000 to about 100,000,and wherein the weight average molecular weight (M_(w)) is from about4,000 to about 500,000, each as measured by gel permeationchromatography using polystyrene standards.
 16. A polythiophene inaccordance with claim 1 wherein A is hexyl heptyl, octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, or pentadecyl.
 17. Apolythiophene in accordance with claim 1 wherein D is an aryleneselected from the group consisting of phenylene, tolylene, xylylene,biphenylene, substituted biphenylene, fluorenylene, phenanthrenylene,dihydrophenanthrenylene, dibenzofuranediyl, dibenzothiophenediyl, andcarbazole-diyl.
 18. A polythiophene in accordance with claim 1 wherein Dis saturated linkage selected from the group consisting of alkylene,dioxyalkane, dioxyarene, and oligoethylene oxide.
 19. A polythiophenewherein the monomer segments thereof contain

wherein A is a side chain; B is hydrogen or a side chain; and D is adivalent segment, and wherein the number of A-substituted thienyleneunits (I) in the monomer segments is from about 1 to about 10, thenumber of B-substituted thienylene units (II) is from 0 to about 5, andthe number of divalent segments D is 1.